Indicating apparatus



June 4, 1940. c. s. DRAPER INDICATiNG APPARATUS Original Filed Jan. 2, 1934 2 Sheets-Sheet 1 June 4, 1940. c. s. DRAPER INDICATING APPARATUS 2 Sheets-Sheet 2 Original Filed Jan. 2, $934 kmxtwb QQ Q MWmQKRBU m bx XBQW S p wymtmbbu m Patented June 4, W40

INDICATING APPARATUS Charles S. Draper, Paio Alto, Calif., asslgnor to Research Corporation, New York, N. Y., a corporation of New York Application January 2, 1934, Serial No. 704,868 Renewed June 8, 1937 4 Claims.

This invention relates to devices for obtaining. data concerning the operation of various types of engines, pumps or other apparatus having one or more chambers enclosing fluids under substan- 5 tial pressures and more particularly internal combustion engines.

Certain data concerning the operation of internal combustion engines has been obtained by devices which give a direct indication of the pressure within the cylinder of an engine. These devices were of complicated and delicate construction and were inaccurate for various reasons. One of the most recently developed instruments for this purpose is the electric type in which a Wheatstone bridge circuit is employed, two of the arms of which are constituted by stacks of carbon discs. These carbon disc piles are mounted on opposite sides of an arm which is under the influence of the gaseous pressure on a diaphragm. When the gas pressure varies, the pressure on one stack of carbon disc's increases while that on the other stack decreases; this throws the Wheatstone bridge out of balance and causes a current to flow through the battery circuit which is directly proportional to the gas pressure within the cylinder. The accuracy of this instrument was affected by heat in the cylinder of an engine causing deflection of the diaphragm with the re-- sulting pressure upon one of the stacks of carbon discs. Calibration for these thermal deflections was necessary and uncertain.

The present invention contemplates the provision of a device for giving indications of the rate of change of pressure in a cylinder of an internal 35, combustion engine which furnishes the engineer with important data concerning the operation of the engine some of which were not'furnished by the devices giving a direct indication of the pressure. The device of the invention is of 40 simple and rugged construction and its accuracy is not aife'cted by those thermal deflections which made calibration of the above mentioned electric instrument necessary and uncertain.

In its broad aspect, the invention contemplates the provision of a device for inducing a voltage upon a conductor or electrical coil in response to changes in pressure within a cylinder of an internal combustion engine and then obtaining a measure of the induced voltage by the use of an indicating instrument selected in accordance with the data desired concerning the operation of the engine. The device is constructed to provide a substantially constant magnetic field in which is positioned a coil adapted to receive an induced 65 voltage. A diaphragm or equivalent element is arranged to be subjected to and oscillated in response to changes in pressure within the engine cylinder. This diaphragm is associated with a member movable therewith and. positioned in the magnetic field. Consequently, the movement or the diaphragm effects changes in the flow of magnetic flux relative to the coil causing a voltage to be induced upon the latter. The output voltage of the coil may operate the indicating or recording instrument directly or through a prop- 5 er vacuum tube amplifier.

The invention will be more clearly understood from the following description in conjunction with the accompanying drawings, in which:

Fig. l is a sectional elevational view of a device 19 embodying the invention;

Fig. 2 is a sectional view taken upon the line 2-2 of Fig. 1;

Fig.3 is a detail view, partly in section, of a portion of the device; 15 Fig. 4 is a diagrammatic view showirig the device assembled upon an internal combustion engine and hooked up to an indicating or recording instrument for giving a record of the rate of change of pressure within the engine cylinder;

Fig. 5 is a plan view of a photographic film upon which a record has been taken in the apparatus illustrated in Fig. 4; and

Fig. 6 is a diagrammatic view showing the device assembled upon an internal combustion en- 25 glue and hooked up with an instrument or meter having a long time constant.

Before explaining in detail the present invention itis to be understood that the invention is not limited in its application to the details of con- 30 struction and arrangement of parts illustrated in the accompanying drawings, since the invention is capable of other embodiments and of being practiced or carried out in various ways. Also it is to be understood that the phraseology or terminology employed herein is for the purpose of de-' scription and not of limitation. and it is not intended to limit theinventlon claimed herein beyond the requirements of the prior art.

The embodiment of the invention illustrated in 40 the accompanying drawings, referring particularly to Figs. 1 to 3 inclusive. comprises a ferrous metal casing ill of general hollow cylindrical form. A cylindrical core ll of iron is positioned within the casing and is provided at its upper end with an annular flange l2 adapted to rest upon a shoulder it formed upon the interior wall of the casing. The core ii is provided with'a small longitudinal passage it. A block of insulating material i5 is suitably held upon the outer end of the core II by screws lt'passing through the same and engaging the annular flange l2. The block it is provided with a longitudinal passage ll registering with the longitudinal passage M in the core H. The core II is held in position within the casing by a member 18 surrounding the block l5 and engaging an internal threaded portion l9 near the upper end of the casing. An annular projection 20 is formed upon the interior wall of the casing adjacent the lower end of the so internal combustion engine.

with a pillar 36 projecting therefrom into the,

core so as to provide an air gap 2| between the core and projection. rounds the core I and is supplied with electrical energy through leads 23 and -24 passing through openings 25 in the casing toa suitable source of electrical supply. Atube of copper or other electrical conductor is fixed in the passage I! of the block l5 so as to project therefrom; If desired, an air supply tube 3| may be fixed upon the outer end of the tube 30 so as to supply cooling air to the interior of the device, the air being exhausted through passages 32iormed in the casing l0.

The other end of the casing I6 is provided with a threaded portion 33 adapted to be received in a threaded opening in the cylinder head of an The edge of a metallic diaphragm 35 is embedded in the casing near the end of the threaded portion 33 to form a gas tight seal therebetween and is provided member 38 is held upon the pillar 36 between a shoulder 39 thereon and a nut 40 engaging the threaded portion 31. The member 38, in the embodiment illustrated, is'constructed of a light f 38 between the same and the coil 42.

non-ferrous metaLsuch as magnesium, and carries coil 42 of copper wire, a coating of a suitable insulating material being applied to the member The length of the air gap 2| is so adjusted in relation to the length of the coil 42 that the coil will be in a region of uniform flux density throughout. any possible diaphragm deflection. One end of the coil 42 is electrically connected with the member 38. The other end of the coil 42 is extended 38 and thence through the passages l4 and H and the tube 30 is connected with a bindingpost 45 upon the'tube 30.

Fig. 4 shows the device of the invention operatively positioned in the cylinder head 50 of .an internal combustion engine with the threaded portion 33 engaging a threaded opening in the head 50 so that the diaphragm 35 is directly exposed to the gas pressure within a cylinder 5|. As shown, the leads 23 and 24 from the exciting coil 22 are connected to the opposite terminals of a battery 52. The end 'of the coil 42 which is connected to the member 36 is electrically connected through the pillar 36 and the diaphragm 35 as well as the cylinder head 56 with a binding post 53 upon the latter. The other end of the coil 42 is connected through the binding post 45 and the lead 54 with a grid 9 of an amplifying tube 55. The filament f of the tube 55 is connected through the lead '56 with one terminal of a rheostat 51, the other terminal of which is connected by a lead 58 with one terminal of a battery A. The-other terminal of the battery A is connected with'the filament by a lead 59.

with one terminal of a battery B'.- The other terminal of the battery 3' is connected by a lead 66 with one terminal of the coil 61 of a galvanometer G which is carried within an L-shaped mounting M of an oscillograph from which natural light is excluded. A resistance 66 is imposed An exciting coil 22 sur-' casing I0 and thence across the air gap 2|.

-positioned in the cylinder head internal combustion engine so that the diaacross the leads 64 and 66. The lead 63 is connected by a lead 69 with the other terminal of the coil 61 of the galvanometer G.

The mounting M has a camera C suitably secured thereto. A drum 12 is mounted within the camera and is rotated by mechanism (not shown) in synchronism with the crank shaft of the internal combustion engine. A photographic film I3 is led from a suitable supply roll over the drum I2 and is driven by the latter in synchronism with the crank shafl; of the internal combustion engine. The light rays from. a suitable source of light, such as a lamp L, are concentrated upon the photographic film 13.

It will be apparent that the oscillation of the diaphragm 35 in response to changesdn pressure within the cylinder 5| will produce oscillation oi" the member 38 and coil 42 in the air gap 2|. The coil 22 creates a fiow of magnetic fiux in a circuit through the wrought iron core II, 'the y proper selection of mass and elastic constants for the diaphragm 35, pillar 36 and member 38 as well as the coil 42, the velocity of the coil 42 may be made to depend directly upon the rate of change of gas pressure within the cylinder 5|. The oscillation of the coil 42 in the magnetic field between the poles of the electromagnet causes a voltage to be induced in the coil. This induced voltage is amplified by the amplifying tube 55 and impressed upon the coil 61 of the galvanometer G to cause oscillation of the mirror I! which in turn reflects-the light rays from the lamp L upon the photographic film 13 to produce a record of the change of pressure as shown by the curve 16 upon the film 13 in Fig. 5.- It will be noted that the curve 16 not only gives a record of the maximum rate of change of pressure but also gives an indication of the changes in pressure due todetonation as shown by the waves 11.

The device of the invention supplying an indication of the rate of change of pressure, as exrise which not only is dependent upon certain characteristics of the engine but also upon the character of the fuel employed and should be restrictedto a certain range for satisfactory engine operation. The rate of change of pressure indication also'enables'the, engineer to determine the crank angle at which maximum pressure occurs and this should take place within a narrow range for best engine output. It gives an indication of the presence or absence of pressure waves within the cylinder, that is, whether or not detonation exists. It also gives an indication of the intensity of detonation if it exists.

The construction of the device of the invention is rugged and simple and requires no close fits or uncertain calibration for zero pressure. -In the embodiment specifically illustrated, theoutput voltage of the coil 42 is always directly proportional to the coil velocity, that is, the characteristic is linear.

meter. The device of the invention is operatively 56' of an phragm 35 is directly exposed to the gas pressure within a cylinder 5|. As shown, the leads 23 and 24 from the exciting coil 22 are connected to the opposite terminals of a battery 52'. The end of the coil 42 which is connected to the member 38 is electrically connected through the pillar 35 and the diaphragm '35 as well as the cylinder head with a binding post 53' upon the latter. The other end of the coil 62 is connected through the binding post t5 and the lead 54 with a grid a" 0! an amplifying tube 55'. The filament oi the tube 55' is connected through the lead at with one terminal of a rheostat 51', the other terminal of which is connected by a lead 58 with one terminal of a battery A. The other terminal of the battery A is connected with the filament by ahead 59'. The binding post 53' is connected with the lead 5% by a lead Ell. A resistance ti is connected across the leads lit andfiii'. One terminal of a battery B" is connected with the lead 59 lily a lead 63'. The other terminal of the battery B" is connected with a grid 9'' of the tube 55 by a lead M. The plate p of the tube 55" is connected by a lead $5 with one terminal of-a battery B. The other terminal of the battery 13" is connected by a lead 65 with one end of the heating wire of a vacuum thermo-couple 8i). A resistance 58 is imposed across the leads M and 56'. The lead 63' is connected by a lead 59 with the other end of the heating wire of the vacuum thermocouple so. This thermo-coupie to is connected by the leads ti and 82 to the terminals of a direct current meter 83 having a long time constant. The meter 23' is provided with the usual indicating pointed M adapted to move over a suitable scale so graduated in terms of suitable units representative of the extent of detonation taking place in the cylinder of the engine.

The voltage induced in the coil d2 will e amplifled by the amplifying tube 55' and the amplified voltage will be impressed upon the heating wire of the thermo-coupie so to produce heating depending upon the rate of change of pressure Wihin the cylinder. This heating creates a direct current which indicated upon the meter 33. Due the time constant of the meter 63 the current in thereby in response to the rate of change i in the engine cylinder dctoha't. takes place will 1% small to the current indicated in response the rate of change of pressure the cylinder where detonation takes place. Consequently, when no detonation takes place in the engine the indication. upon the meter at will be small whereas, when detonation takes place the indication will be large. The indication of the meter at gives a measure of the average or root mean square value of the voltage induced in the coil 52 in response to the changes in pressure within the cylinder of the engine and, consequently, the indication is peculiarly valuable as a measure of detonation intensity.

Throughout the appended claims the expression pressure Within the cylinder of an internal combustion engine" is intended to include other types of engines, pumps or other apparatus having chambers enclosing fluids under substantial pressures.

I claim:

1. An apparatus for obtaining a representation of rate of change in pressure within the cylinder oi. an internal combustion engine comprising means for producing a magnetic field, an electrical coil positioned in said field and adapted to receive an induced voltage, and means for causing a voltage to be induced in said coil in response to the rate of change in pressure within said cylinder, and means for integrating the variations in voltage due to the rate of change of pressure within said cylinder during a given period, said means including a meter having a time constant greater than said period. i

2. An apparatus for obtaining a representation of rate of change in pressure within the cylinder of an internal combustion engine comprising means for producing a substantially constant magnetic field, a movable member positioned in said field, an electrical coil carried by said memher and positioned in said field and adapted to receive an induced voltage. a. diaphragm adapted to be subjected to and oscillated response to the rate of change in pressure within said cyllncler, operative connections between said diaphragm and said movable member whereby said coil is moved in said field to cause a voltage to be induced therein responsive to the rate of change in pressure within said cylinder, and means for integrating the variations in voltage due to the rate of change of pressure within said cylinder during a given period, said means including a. meter having a time constant greater than said period.

3. In apparatus for indicating engine detonation by measuring the rate of change of pressure obtaining within an engine cylinder, in combination, a hollow casing arranged to project inwardly through the cylinder head and having inner thick and substantially rigid diaphragm disposed substantially flush with the inner cylinder Wall so as to be directly exposed to the cylinder gases, the rigidity of said diaphragm enabling the same to alone withstand the entire cylinder pressure, and an electromagnetic generator contained within said casing. said generator having a stati part carried by said casing and having a mo part rigidiy supported upon and movable said than ragm, the output of said generator responding to the rate of change of pressc within said cylinder.

In apparatus for indicating rich by measuring the of change obtaining within engine cylinder, in c n c. tion, a hollow casing arranged topi'oiect inwardly through the head having a stiff though elastic diaphragm at its inner end positioned so as to constitute in chest continuation of the inner cylinder wall, said diaphragm of itself withstanding the entire cylinder gas pressure exerted directly thereon, and an electric generator contained within said casing, said generator comprising a coil structure fixedly attached to said diaphragm and providing a coil adapted to receive an induced voltage, a core structure carried by said casing and providing a fiux field for said coil that is of uniform flux density throughout the range of movement of said coil, motion of said coil in said field producing a voltage in said coil proportional to the velocity thereof. the movement of said coil resulting from diaphragm deflection under pressure changes in the cylinder, the elasticity of the mass consisting of said movingcoil structure and diaphragm being confined substantially entirely to said diaphragm.

CHARLES S. DRAPERQ 

